Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 241652 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1151 AM EST WED DEC 24 2014 .SYNOPSIS... LOW PRESSURE TO THE WEST OF THE APPALACHIANS WILL DEEPEN AND LIFT NORTH TOWARD THE GREAT LAKES TODAY. THIS LOW WILL DRAG A COLD FRONT THROUGH THE COASTAL CAROLINAS TONIGHT. DRY HIGH PRESSURE WILL BUILD OVER THE SOUTHEAST CHRISTMAS DAY INTO FRIDAY BEFORE MOVING OFF THE COAST SATURDAY. A COLD FRONT WILL DROP INTO THE SOUTHEAST ON SUNDAY WITH A FEW WAVES OF LOW PRESSURE DEVELOPING MONDAY THROUGH WEDNESDAY NEXT WEEK...LEAVING UNSETTLED WEATHER ACROSS THE CAROLINAS. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1000 AM WEDNESDAY...COMPLEX AND ACTIVE WEATHER ON TAP FOR MUCH OF THE SOUTHEAST ON THIS CHRISTMAS EVE. FULL LATITUDE UPPER TROUGH ALIGNED FROM THE WESTERN GREAT LAKES DOWN INTO EASTERN TEXAS IS SLOWLY DRIFTING EAST THIS MORNING. BENEATH THIS TROUGH...A STRENGTHENING SURFACE LOW IS MOVING NORTH INTO THE GREAT LAKES...AND ALTHOUGH THIS WILL STAY WELL AWAY FROM THE CWA...IT WILL DRIVE A STRONG COLD FRONT ACROSS THE REGION TONIGHT. THE COMBINATION OF WAA AHEAD OF THE COLD FRONT...INCREASING THETA-E RIDGING...AND DIFFLUENCE WITHIN AN UPPER JET WILL CREATE WIDESPREAD SHOWERS WITH ISOLATED TSTMS TODAY. WHILE PRECIP WILL BE WIDESPREAD AND HEAVY AT TIMES...TWO BIG QUESTION MARKS STILL REMAIN...AND THESE ARE WHETHER SEVERE THUNDERSTORMS WILL DEVELOP...AND AT WHAT TIME THE PRECIP WILL END TODAY. KLTX IMAGERY THIS MORNING SHOWS AN AREA OF HEAVIER RAINFALL MOVING ACROSS THE ILM NC COUNTIES...WITH SCATTERED BUT LESS INTENSE SHOWER ACTIVITY TO THE SOUTHWEST. REGIONAL MOSAIC HAS A LINE OF CONVECTION FROM WEST OF COLUMBIA, SC...TO VALDOSTA, GA. HIGH RES HRRR AND WRF SUGGEST A LULL IN PRECIP FOR SEVERAL HOURS THIS AFTN AHEAD OF THE FORCED LINE...AND HAVE TRIED TO SHOW POP TRENDS MIMICKING THIS IDEA. THIS SEEMS PLAUSIBLE SINCE DIFFLUENCE THIS MORNING WILL WEAKEN AND SOME SUBSIDENCE IS LIKELY IN THE WAKE OF THIS MORNINGS ACTION. HOWEVER...ISOLATED THUNDER WILL STILL BE POSSIBLE THROUGH NOON OR SO...ESPECIALLY IN PLACES WHERE TEMPS HIT 70-72F SINCE THAT WILL BE CAPABLE OF TAPPING THE INSTABILITY ABOVE 950MB PRESENT ON THE 12Z KCHS UA SOUNDING. HEAVY RAIN WILL BE THE PRIMARY THREAT THIS MORNING...AND SOME PLACES MAY PICK UP A QUICK 1 INCH OF QPF IN EMBEDDED TSTMS. THEREAFTER...ATTN TURNS TO THE PRE-FRONTAL FORCED LINE AND ITS ANTICIPATED IMPACTS LOCALLY. AS THE LOW PRESSURE MOVES NORTH...THE EASTWARD PROGRESS OF THIS LINE WILL SLOW...AND THEREFORE BELIEVE THE WRF IS TOO FAST IN ITS EVOLUTION...BUT STILL ACCURATE IN ITS OVERALL DEPICTION. SPC SWODY1 HAS THE AREA IN A MARGINAL RISK...WITH A SLIGHT RISK SOUTH OF MYRTLE BEACH...FOR POSSIBLE DAMAGING WINDS AND ISOLATED TORNADOES AS THIS QLCS APPROACHES. LOCALLY THE TORNADO THREAT SEEMS EXTREMELY LOW WITH MLCAPES OF 300 J/KG OR LESS AND 0-3KM SRH REACHING ONLY AS HIGH AS AROUND 200 M2/S2. AT THE SAME TIME...LOW-LEVEL WINDS OF 50 KTS AT 2KFT WILL SLOWLY VEER MORE TO THE SW THIS AFTN...ERODING EVEN FURTHER THE TORNADO THREAT...BUT MAINTAINING A DAMAGING WIND POTENTIAL. WILL HAVE TO MONITOR EVOLUTION OF THIS SQUALL LINE AS IT REACHES THE CWA...AND IT WILL LIKELY DO SO IN A WEAKENING STATE...BUT CANNOT RULE OUT AN ISOLATED DAMAGING WIND GUST THIS EVENING. A LARGE AREA OF TRAILING STRATIFORM RAIN WILL PERSIST BEHIND THE SQUALL LINE...AND THUS EVEN THOUGH THE COLD FRONT DOES NOT CROSS THE CWA UNTIL AFTER MIDNIGHT...IT WILL HAVE DIFFICULTY DEVELOPING ANY CONVECTION OTHER THAN SHALLOW SHOWERY TYPE PRECIP. HIGHS TODAY WILL RISE INTO THE LOW 70S MOST AREAS EVEN WITHOUT ANY SUNSHINE THANKS TO STRONG WAA. TEMPERATURES WILL BEGIN TO CRASH BEHIND THE COLD FRONT AFTER MIDNIGHT...BUT ONLY A FEW HOURS OF COOLING BEFORE DAYBREAK WILL LIMIT MINS TO AROUND 50 WELL INLAND...AND NEAR 60 RIGHT ALONG THE COAST. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 AM WEDNESDAY...A COLD FRONT WILL BE PUSHING FARTHER OFF SHORE THROUGH THURS AS HIGH PRESSURE BUILDS UP FROM GULF COAST. ANY LINGERING PCP OR MOISTURE WILL BE SCOURED OUT AS MID TO UPPER TROUGH MOVES EAST LEAVING A DEEP DRY AND COOLER W-NW FLOW BEHIND IT. EXPECT PCP WATER VALUES DOWN FROM UP NEAR 2 INCHES THE NIGHT BEFORE TO A QUARTER OF INCH BY THURS AFTERNOON AS COLUMN DRIES OUT. OVERALL EXPECT CLEARING SKIES ON CHRISTMAS DAY WITH SUNSHINE MAKING AN APPEARANCE FOR THE FIRST TIME IN SEVERAL DAYS. TEMPS SHOULD NOT MOVE MUCH ON THURS AS A WARM START TO THE DAY WILL BE FOLLOWED BY GUSTY W-NW WINDS BRINGING IN RELATIVELY COOLER AIR. MODELS HAVE BEEN CONSISTENTLY BACKING OFF ON CAA BEHIND THE FRONT WITH 850 TEMPS ONLY FALLING ABOUT 6 C BEHIND FRONT BEFORE LEVELING OFF AND RISING SLIGHTLY THROUGH FRI. TEMPS THURS NIGHT SHOULD BE DOWN IN THE 30S AND BASICALLY EXPECT SEASONABLE TO ABOVE NORMAL TEMPS IN THE FORECAST AS HIGH PRESSURE BUILDS UP FROM THE GULF COAST OVER THE SOUTHEAST THROUGH FRI. THE CENTER OF THE HIGH ALMOST DIRECTLY OVERHEAD FRI AFTN WILL SHIFT OFF SHORE BY FRI NIGHT LEAVING A LIGHT RETURN FLOW. THIS WILL HELP TO CAUSE A SLIGHT RISE IN DEWPOINT TEMPS AND THEREFORE WILL KEEP TEMP A BIT HIGHER THAN THE NIGHT BEFORE BUT THE WINDS WILL BE LIGHT ENOUGH UNDER CLEAR SKIES TO PRODUCE DECENT RADIATIONAL COOLING. THIS WILL BRING TEMPS DOWN CLOSER TO 40 FOR FRI NIGHT. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 330 AM WEDNESDAY...RIDGE OF HIGH PRESSURE UP THE SOUTHEAST COAST ON SATURDAY WILL SHIFT EAST THROUGH EARLY NEXT WEEK. THIS WILL ALLOW A RETURN FLOW TO SET UP WITH SW-W WINDS THROUGH THE LOW TO MID LEVELS OF THE ATMOSPHERE. INITIALLY SHOULD SEE A FAIR AMOUNT OF SUNSHINE ON SATURDAY BUT A COLD FRONT WILL DROP SOUTH ON SUNDAY LEAVING SHALLOW COOL AIR IN PLACE. SHOULD SEE CLOUDS AND PCP SPREAD OVER THE CAROLINAS SAT NIGHT INTO SUNDAY AS COLD FRONT DROPS SOUTH WITH SOME DECENT ISENTROPIC LIFT DEVELOPING. THE GFS AND ECMWF SHOW A FEW WAVES OF LOW PRESSURE MOVING UP FROM THE GULF COAST ALONG THIS FRONT THROUGH NEXT WEEK. MAY END UP WITH AN EXTENDED PERIOD OF UNSETTLED WEATHER AS POSSIBLE WEDGE SETS UP. TEMPS ON SAT INTO SUNDAY SHOULD REMAIN ON THE WARM SIDE WITH 60S MOST PLACES. SOME UNCERTAINTY EXISTS WITH LOCATION OF COLD FRONT AS ECMWF KEEPS IT NORTH AND SHOWS WAVES OF LOW PRESSURE MOVING ALONG FRONT TO THE NORTH OF LOCAL AREA. THIS COULD KEEP LOCAL AREA IN WARMER SW FLOW AT THE SURFACE WITH WEDGE HOLDING INLAND AND TO OUR NORTH. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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AS OF 18Z...MODERATE TO HEAVY PRECIP WILL OCCUR THROUGH MUCH OF THE AFTERNOON WITH ISOLATED THUNDER. THE COASTAL TERMINALS ARE BOUNCING FROM IFR TO MVFR WITH STRONG SOUTH SOUTHWESTERLY FLOW. MODELS ARE IN REASONABLE AGREEMENT WITH THE HEAVIEST ACTIVITY THIS AFTERNOON...FOLLOWED BY LIGHTER PRECIP ALONG THE FRONT THIS EVENING. THE FRONT WILL REACH THE COAST THROUGH THE OVERNIGHT HOURS. LOOK FOR A WIND SHIFT TO THE WEST...POST FRONTAL. SKIES SHOULD IMPROVE FAIRLY RAPIDLY TO VFR BEHIND THE FRONT WITH GUSTY WEST WINDS DIMINISHING SOMEWHAT SHORTLY AFTER DAYBREAK. EXTENDED OUTLOOK...VFR THURSDAY THROUGH SATURDAY. RAIN RETURNING SUNDAY AND POSSIBLY MONDAY.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 1000 AM WEDNESDAY...TROPICAL AIRMASS BEHIND A WARM FRONT NOW SITUATED WELL INLAND IS ADVECTING INTO THE WATERS THIS MORNING...WITH DEWPOINT TEMPERATURES APPROACHING 70...OR EVEN THE LOW 70S. THESE DEWPOINT TEMPS ARE 15 DEGREES ABOVE THE COOL SHELF WATER TEMPS...WHICH IS TYPICALLY A SIGNAL FOR SEA FOG. ATTM HOWEVER...NO VSBY RESTRICTIONS HAVE BEEN NOTED AND IT MAY BE SIMPLY DUE TO THE STRENGTH OF THE WIND FIELDS NOT ALLOWING FOR AMPLE PARCEL RESIDENCE TIME. STILL...THE MARINE DENSE FOG ADVISORY REMAINS AND WILL CONTINUE AS THERE REDUCED VISIBILITY IN MARINE FOG IS STILL EXPECTED TO DEVELOP UNTIL THE COLD FRONTAL PASSAGE TONIGHT. SHOWER ACTIVITY WILL BE SCATTERED THROUGH THE AFTN AND EVE...BEFORE A MORE STRONGLY FORCED SQUALL LINE WILL CROSS THE WATERS THIS EVENING AND TONIGHT. WINDS WILL BE GUSTY TODAY EVEN OUTSIDE OF CONVECTION...AND THE CURRENT SCA REMAINS UNCHANGED FOR BOTH WINDS AND SEAS...WHICH ARE ALREADY APPROACHING 7 FT AT WILMINGTON HARBOR BUOY. A WIND SHIFT TO THE WEST WILL OCCUR WITH THE FROPA...WHICH IS EXPECTED AFTER MIDNIGHT. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 AM WEDNESDAY...COLD FRONT WILL SHIFT FARTHER OFF SHORE ON THURS AS HIGH PRESSURE BUILDS UP FROM THE GULF COAST. GUSTY W-SW WINDS EARLY THURS WILL VEER AROUND BECOMING WEST THROUGH THE DAY. SEAS UP AROUND 5 TO 7 FT SHOULD FALL BELOW SCA THRESHOLDS BY THURS AFTN WITH HIGHEST SEAS GETTING PUSHED FARTHER OFF SHORE IN STRONGER W-NW FLOW BEHIND FRONT. WINDS WILL VEER FURTHER TO THE NW AND LIGHTEN UP LATE THURS INTO FRI AS CENTER OF HIGH SHIFTS CLOSER OVERHEAD. SEAS WILL BE DOWN TO 2 TO 4 FT BY THURS NIGHT AND DOWN TO 3 FT OR LESS THROUGH FRI AS HIGH PRESSURE MOVES OVERHEAD WITH MORE VARIABLE WINDS EXPECTED. LONG TERM /SATURDAY THROUGH SUNDAY/... AS OF 330 AM WEDNESDAY...HIGH PRESSURE WILL SHIFT FARTHER OFF SHORE ON SATURDAY WITH A RETURN FLOW S-SW 10 KTS OR LESS SETTING UP. A COLD FRONT WILL DROP SOUTH SUN WITH POSSIBLE WEDGE DEVELOPING WITH WINDS VEERING AROUND TO THE N-NE AS IT DROPS SOUTH SUN NIGHT. THIS WILL PUSH SEAS UP A BIT BUT OVERALL BUT EXPECT SEAS TO GENERALLY 3 FT OR LESS THROUGH THE PERIOD. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...DENSE FOG ADVISORY UNTIL 6 PM EST THIS EVENING FOR AMZ250-252- 254-256. SMALL CRAFT ADVISORY UNTIL NOON EST THURSDAY FOR AMZ250-252- 254-256. && $$ NEAR TERM...17 SHORT TERM...RGZ LONG TERM...RGZ AVIATION...43

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